Comments on Saliva vs Serum Testing in People
Saliva hormone or food antigen testing is a new technology. It's been used only in the last decade and, therefore, is not yet widely accepted by the medical community. Saliva testing also is not readily available in many laboratories. Furthermore, there's room for human error when gathering the saliva sample, as food or blood can easily contaminate the specimen.
The good news is saliva collection is noninvasive, painless, relatively inexpensive and convenient for the patient. When comparing saliva and serum methods, published studies have shown a saliva sample is more accurate than a serum sample.
For this reason, measurement of saliva IgA, IgG, and IgM antibodies against specific antigens of foods, intestinal bacterial and fungal flora is of considerable importance in the pathogenesis of immunologically mediated diseases, including food allergies or intolerance and autoimmunities.
Secretory IgA is capable of functioning as a blocking antibody, which can create a barrier to certain macromolecules, bacteria, and viruses. The interaction with secretory IgA will not permit such antigens to interact with the mucosa and blocks their entrance and exposure to the gut-associated lymphoid tissue. This blockage permits the host to shield efficiently the systemic immune response, local immune response, or both, from being bombarded by many molecules. An additional role of secretory IgA is prevention of diffusion of food antigens into mucous membranes.
Unlike the immediate effects of IgE-mediated allergy, the IgG and IgA-mediated food allergy and intolerance reactions can take several days to appear. Levels of IgG and IgA antibodies in the blood against different food antigens have been used for demonstration of delayed food allergy and intolerance reactions. Therefore, raised serum or plasma IgG and IgA levels of food-specific antibodies are often associated with food allergies. However, measurement of IgG or IgA in the blood may miss abnormal immune reaction to many food antigens. In one instance, it is known that oral or intragastric administration of dietary soluble proteins such as bovine gammaglobulin (BGG) and ovalbumin or egg albumin results in salivary IgA production, but not in any antibody production in serum.
The deposition of antigens in the gut has been shown to lead to the production of IgA antibodies in secretion at sites distant from the gut, such as colostrums, lacrimal and salivary secretions in man and salivary secretions in rhesus monkeys and in rats.
A general conclusion, therefore, is that the secretory immune system can be stimulated centrally and that precursors of IgA-producing cells migrate from the gut-associated lymphoid tissue to several secretory sites in addition to the lamina propria of the gut itself. Therefore, if antigens are injected into the submucosal tissues, they are likely to induce serum IgG antibodies as well as secretory IgA antibodies in saliva. However, if it is applied topically to the skin or to the intraepithelial tissue, secretory IgA is the main product, which is detected in saliva. The role of topically applied antigen in the localization and persistence of IgA responses has been demonstrated in several secretory sites, including the respiratory tract, oral cavity, gut and vagina. |